1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a discharging method of an in-plane switching mode liquid crystal display panel for removing stain due to static electricity generated in processing the liquid crystal display panel.
2. Description of the Related Art
Generally, a twisted nematic mode liquid crystal display (LCD) device mainly used as a flat panel display device of high picture quality and low electric power consumption has a narrow viewing angle. This narrow viewing angle is due to a refractive anisotropy property of liquid crystal molecules. The refractive anisotropy of the liquid crystal molecules is itself caused by a change in an orientation of the liquid crystal molecules when a voltage is applied to a liquid crystal display panel. Specifically, the liquid crystal molecules originally aligned in a horizontal direction with respect to a substrate are subsequently aligned vertically with respect to the substrate when the voltage is applied to the liquid crystal display panel. Accordingly, in-plane switching mode liquid crystal display devices are actively being investigated to solve the viewing angle problem by aligning the liquid crystal molecules horizontally with respect to the substrate.
FIG. 1 is an in-plane switching mode LCD device in accordance with the related art. As shown in the FIG. 1, a gate line 1 and a data line 2 are arranged horizontally and vertically, respectively, on a transparent substrate to define a pixel region. In a typical liquid crystal display device, N gate lines 1 and M data lines 2 are crossed to define an array of N×M pixels. However, in FIG. 1, only one pixel is shown for a simplicity.
A thin film transistor T is disposed at an intersection of the gate line 1 and the data line 2. A common line 3 is disposed in the pixel region in parallel with the gate line 1. Moreover, at least a pair of electrodes, specifically, a pixel electrode 8 and a common electrode 9, are formed in the pixel region. The pixel electrode 8 and the common electrode 9 are arranged in parallel with each other for switching the liquid crystal molecules. The pixel electrode 8 is connected to a drain electrode 6b of the thin film transistor T, and the common electrode 9 is connected to the common line 3. Accordingly, an external voltage is applied across the thin film transistor T to generate a lateral electric field between the pixel electrode 8 and the common electrode 9.
FIG. 2A depicts the deposition of a first metal layer as a processing step in a fabricating method of an in-plane switching mode LCD device in accordance with the related art. As shown in FIG. 2A, a first metal layer is deposited on a first transparent substrate 10 by a sputtering method. Thus, the first metal layer is photo-etched to form a gate electrode 5 and a common electrode 9.
FIG. 2B depicts the deposition of amorphous silicon as a processing step in a fabricating method of an in-plane switching mode LCD device in accordance with the related art. As shown in FIG. 2B, SiOx or SiNx, amorphous silicon (a-Si), and impurity amorphous silicon (n+ a-Si) are subsequently deposited to form a gate insulating layer 12, a-Si layer 15a, and n+ layer 16a. 
FIG. 2C depicts a patterning step in a fabricating method of an in-plane switching mode LCD device in accordance with the related art. As shown in FIG. 2C, the a-Si layer 15a and the n+ layer 16a are subsequently patterned to form a semiconductor layer 15 and an ohmic contact layer 16.
FIG. 2D depicts a step of depositing a second metal layer in a fabricating method of an in-plane switching mode LCD device in accordance with the related art. As shown in FIG. 2D, a second metal layer is deposited and patterned to form a source electrode 6a, a drain electrode 6b, and a pixel electrode 8. Then, a passivation film 20 is formed entirely thereon. The passivation film 20 in the pixel region is thereafter removed in order to strengthen the intensity of a lateral field applied between the common electrode 9 and the pixel electrode 8.
FIG. 2E depicts an alignment processing step in a fabricating method of an in-plane switching mode LCD device in accordance with the related art. As shown in FIG. 2E, a first alignment film 23a is subsequently deposited on the entire substrate. Subsequently, an alignment process is performed on the first alignment film 23a in order to fabricate a thin film transistor substrate 40. Moreover, a black matrix 28 is formed on a second transparent substrate 12 to prevent leakage of light to the thin film transistor T, the gate line, and the data line. Furthermore, a color filter layer 29 is formed thereon, and a second alignment film 23b is deposited on the entire substrate to fabricate a color filter substrate 50. Thereafter, a liquid crystal is injected between the thin film transistor substrate 40 and the color filter substrate 50 to form a liquid crystal layer 30.
When the device is completed by the aforementioned processes, an electric test is performed to detect opened or shorted lines. In this respect, a partial charge may be generated within the substrate by frequent movements of the liquid crystal display panel attached by the thin film transistor substrate and the color filter substrate. If a charged region is generated within the thin film transistor substrate, the liquid crystal may not be properly driven in the charged region during an automatic lighting test, thereby generating a stain on an image. The stain is called electrostatic stain.
FIG. 3 is a sectional view of a normally driven liquid crystal display device. As shown in FIG. 3, in the absence of a charged region within the thin film transistor substrate, the liquid crystal display device is normally driven. Accordingly, if a voltage is applied between the pixel electrode 8 and the common electrode 9, a lateral field having a constant direction is generated therebetween. Accordingly, the liquid crystal is twisted towards the field direction in accordance with an intensity of the applied voltage.
FIG. 4 is a sectional view of an abnormally driven liquid crystal display device due to a back surface charge of a thin film transistor in accordance with the related art. As shown if FIG. 4, when a partial charge is generated at the back surface of the thin film transistor substrate by frequent movements of the substrate during processing, the charged region 32 distorts the electric field between the pixel electrode 8 and the common electrode 9. Accordingly, the liquid crystal aligned near the charged region is not normally driven but generates a stain on the image during lighting. Accordingly, because the lighting test is performed in a state where the liquid crystal display panel is not completely discharged, a picture quality is greatly influenced during the lighting test, thereby preventing accurate detection of defects in the liquid crystal display panel.